Impulse generating system



Nov. 20, 1951 G. B, PARKINSON IMPULSE GENERATING SYSTEM 2 SHEETS-SHEET 1Filed Jan. 22, 1946 3mm GEOFFREY B. PAR'KINSON Nov. 20, 1951 3, 5,PAKINSQN 2,575,559

IMPULSE GENERATING SYSTEM Filed Jan. 22, 1946 2 SHEETS-SHEET 2 A n F1 020 4'0 66 do 160 IZIO I40 lo GRID PULSE AMPLITUDE (VOLTS) GEOFFREYPARKINSON Patented Nov. 20, 1951 I IMPULSE GENERATING SYSTEM Geoffrey B.Parkinson, Washington, D. 0;, assignor to the Minister of Supply in HisMajestys Government of the United Kingdom of Great Britain and NorthernIreland, London,

England Application J anuary 22, 1946, Serial No. 642,695

7 Claims.

This invention relates in general to an impuls generator andparticularly to a gas tube type of impulse generating system.

It is an object of this invention to provide a simple, eflicient, ultrashort duration impulse generating system.

It is another object of this invention to provide a method of and meansfor producing voltage impulses a fraction of a microsecond in duration.

It is another object of this invention to provide a system of theforegoing type for producing voltage impulses of a selectable duration.

Other objects and features of the present invention will become apparentupon a careful consideration of the following'detailed description whentaken drawings.

Fig. 1 is a detailed circuit diagram of one embodiment of the invention;

Fig. 2 is a detailed circuit diagram of a'variant embodiment of theinvention;

Figs. 3 and 4 show a series of waveforms useful in explaining theoperation of Figs. 1 and 2 respectively, and

Fig. 5 shows a series of curves illustrating the starting timecharacteristic of a pair of well known gas tubes.

In the operating characteristics of grid controlled gas tubes, I havediscovered that the ignition time of such tubes is determined by thetrigger signal amplitude applied'to the tube'grid as well as by ambienttemperature and plate voltage. Specifically, I have discovered thatignition time varies inversely with grid signal amplitude. Advantage istaken of this phenomena in practicing the present invention. Briefly,the system provided by the present invention comprises at least one gastube arranged in such a manner that ignition thereof generates thetrailing edge of the pulse. The time duration of this pulse isdetermined by the ionization time of the gas'tube, and is controlled byadjustment of the trigger signalamplitude applied to the gas tube. r

In the two embodiments of the invention which are herein illustrated, apair of gas tubes are employed. The first is arranged to produce, uponignition, the leading edge of a pulse and the second is arranged toproduce the trailing edge of the pulse, upon ignition. The triggersignal for the second tube is produced by and obtained from the firsttube in such a manner that pulse duration may be controlled byselectively varying the amplitude of the triggering together with theaccompanying signal applied to the second tube. Incorporated in theinvention is a suitable device for quenching the two gas tubes once theoutput pulse has been produced. For purposes of illustration this devicehas been represented as an artificial transmission line. It is to beunderstood, however, that any other suitable device may be used, ifdesired. It is also to be understood that even though I have shown twogas tubes as constitilting the preferred embodiments of the invention; atube other than that of the gaseous variety, or other suitable devicemay be used to generate the leading edge of the pulse.

Reference is now had in particular to Fig. i where one typicalembodiment of the invention is shown. The two gas tube components whichcomprise, in part, the circuit of the invention are illustrated at [0and II, and as herein indicated are connected together at their anodesby lead 2|. In the quiescent state of the circuit both tubes are biasednon-conducting and therefore consume no idle current. Bias for the firsttube I0 is represented as a negative voltage [8 applied to the tube gridvia resistance is. Bias for the'second tube H is represented as apositive voltage l3 applied to the cathode of the tube. The first tubeIn is plate loaded by resistance 20, and cathode loaded by theresistance of potentiometer 22. Across the latter resistance the outputterminals I5 of the circuit are taken. The tube quenching device isrepresented as an open circuited transmission line It connected to theanodes of the tubes.

From the foregoing paragraph it becomes obvious that in order toinstitute the generation of a voltage pulse by igniting tube IE3, apositive trigger pulse must be applied to the tube grid via the inputterminals l1. Upon the application of such a triggering pulse, tube IE!fires and line It, which is normally charged, commences to discharge atsteady rate through the tube and the resistance of potentiometer 22. Atthis instant the voltage across the resistance of potentiometer 22' andhence the voltage across the output terminals 15 rises abruptlypositive. The leading edge of the output pulse is thus formed. A-selectable portion of the voltage wavefront appearing acrosspotentiometer 22 is communicated via movable arm M to the control gridof tube H. A fraction of a microsecond later, depending uponthe settingof movable arm at, tube i! will ionize and the potential at the'anodesof the tubes will fall abruptly negative to substantially that of thesource indicated at [3, which is only a few volts positive of ground. Atthe same in- 3 stant the voltage appearing across potentiometer 22 fallsabruptly to some voltage slightly less positive than source l3. Thisaction generates the trailing edge of the impulse.

To quench the tubes, the reflection qualities of the artificial line Itare utilized. In brief, as tube I is rendered conducting, current fiowsout of the line and through the tube. This current represents thecurrent of a positive voltage wave propagating in the same direction,right to left, along the line. Then if the line is terminated at thetube end, (essentially the resistance of potentiometer 22) in someimpedance less than its characteristic impedance, reflection withinversion will occur and. the net result will be an abrupt drop involtage at the anodes of the tubes. By selecting a value of resistancefor potentiometer 22 something less than the characteristic impedance ofthe line the incident wave will be inverted, made negative in this case,and reflected back down the line to the open circuited end. At the opencircuited end the wave will again be reflected, this time withoutinversion. Then after a time delay determined by the equivalentelectrical length of the line this negative reflected wave will reachthe tube end of the line. In the meantime, however, tube H -has beenfired and the voltage existing at the anodes of the tubesis-substantially equal to the source 13 so that the reflected negativewave will actually drive the anodes negative relative to ground tothereby quench both tubes simultaneously. As afore-mentioned anysuitable arrangement may be used to quench the tubes, but an artificialline is preferred because of its compactness, rapid action, and constantdischarge rate as beneficial to pulse definition.

From close observation of the circuit in Fig. 1 it will be recognizedthat the value of plate resistance 2B is selected so that the timeconstant formed by it and the capacitance of line [6 is great enough tohold the tubes anodes negative relative to ground long enough to permitdeionization to occur.

To facilitate a comprehensive understanding of the exact action of thecircuit in Fig. 1 during a cycle of operation, reference is now had tothe waveforms shown in Fig. 3. In Fig. 3, time is plotted along thehorizontal axis and voltage along the vertical axis. Waveform Arepresents a trigger signal applied to tube Ill via input terminals l'i.Waveform B represents the voltage variation which occurs at the anode ofthe tubes in response to the trigger signal shown in waveform A. Asshown by waveform B the voltage at the anodes of the tubes dropsabruptly from 13+ coincident with the leading edge of the triggersignal. This is due to the fact that the incident wave propagating alongline it is inverted and reflected by the mismatch in terminatingimpedances at the tube end of the line. As shown in waveform C, whichrepresents the signal appearing across the output terminals l5, ignitionof tube It! generates the leading edge F of the output pulse. A shorttime thereafter tube fires and the anode voltage for the tubes dropsabruptly negative to substantially the voltage of source voltage I3.This action is represented by reference character G in waveform B.

At this instant the trailing edge of the output pulse shown in wave formC is generated. Thereafter the negative wave reflected from the open endof the line returns to the tube end of the line and drives the anodesabruptly negative relative to ground, as shown at H in waveform B.

4 The tubes deionize and the line starts to recharge through resistance20 to produce the exponential rise of the anode voltage indicated at I.

From the foregoing it may be clearly recognized that the time ofduration of the output pulse depends on the ignition time of tube H.

In Fig. 5, to which reference is now had, the ignition timecharacteristic versus grid signal amplitude of a pair of gas tubes isshown. In particular curves X and Y typify the ignition timecharacteristic of a 2050 type of gas tube. Curve X represents theignition time of this tube with 120 volts at its anode and 10 voltscathode bias. Curve Y represents the ignition time of this tube with 600volts at its anode and 16 volts cathode bias.

Curve Z represents the ignition time of an 884 type of gas tube withvolts at its anode and 15 volts cathode bias. The ignition time, asherein indicated, decreases inversely with the trigger signal amplitude.Consequently the movable arm M of potentiometer 22, through which thetrigger signal for tube H is communicated, provides an ideal control ofimpulse duration.

In the embodiment of Fig. 1 the action of line It was such as tosimultaneously quench both tubes. If, however, it is desired to havetube H quench tube l0 and the line 16 quench tube H the arrangementshown in Fig. 2 may be employed. Herein reference characters similar tothose used in Fig. 1 are employed to designate corresponding elements inthe two circuits. The major difierence in the circuits of Fig. 1 andFig. 2 is that the grid of tube H is A. C. coupled to the movable armHl'of potentiometer 22, thus permitting the cathode of tube II to bereturned to a negative potential 24. Bias for tube II, in this case isprovided by a negative voltage'indicated at 23 and applied to its grid.

The action of Fig. 2 is essentially the same as that of Fig. 1 excepttube It in this case is deionized as tube 1 i is ionized, and theimpulse generated at terminals 15 contains a trailing edge that fallsabruptly to ground or slightly below ground depending on the cathodebias of tube H. The waveforms illustrating the action of Fig. 2 areshown in Fig. 4. Herein, waveform A again represents the trigger signalapplied at terminals ll. Waveform B represents the anode voltagevariation in response to the trigger signal of wave form A. Fromwaveform B it will be recognized that as tube H fires, the anode voltageof the tubes drops abruptly to ground or slightly below ground (asindicated by portion G) depending on the cathode bias of tube H. Hencetube ill will deionize in response to ionization of tube ii, while thelatter tube will again deionize in response to the negative reflection(as indicated at H) from line l6. Waveform C again represents the signalimpulse generated at the terminals 15.

Although I have shown and described only limited and specificembodiments of the present invention I am fully aware of the manymodifications possible thereof. Therefore this invention is not to berestricted except insofar as is necessitated by the spirit of the priorart and the scope of the appended claims.

What is claimed is:

l. A gas tube generator comprising, a source of operating potential,first and second grid controlled gas tubes connected together at theiranodes and to said source of operating potential, an impedance elementconnected to said first tube and across which output terminals for thecircuit are taken, an artificial line connected to said tubes forquenching the same, the grid of said second tube so associated with saidoutput terminals as to receive a selectable amplitude of the signalvariation which appears thereacrosswhen said first tube is renderedconducting, and means for impressing a triggering signal to the grid ofsaid first tube.

2. A gas tube generator comprising, a source of operating potential,first and second grid controlled gas tubes connected together at theiranodes and to said source of operating potential, an impedance elementconnected to said first tube and across which output terminals for thecircuit are taken, an open circuited artificial line connected to theanodes of said tubes for quenching the same, the grid of said secondtube so associated with said output terminals as to receive a selectableamplitude of the signal variation which appears thereacross when saidfirst tube is rendered conducting, and m ans for impressing a triggeringsignal to the grid of said first tube.

3. A pulse generator comprising, a source of operating potential, firstand second grid controlled gas tubes connected to said operatingpotential, an output circuit connected to said first tube to receive anabrupt potential variation of one sense in response to conduction bysaid first tube, and further connected through said first tube to saidsecond tube to receive an abrupt variation in potential of the oppositesense in response to conduction by said second tube, means for applyinga triggering signal to the grid of said first tube, and means forapplying a controllable amplitude triggering signal to the grid of thesecond tube simultaneously with the establish} ment of conduction insaid first tube.

4. A pulse generator comprising, a source of, operating potential, firstand second grid controlled gas tubes connected to said operatingpotential, an output circuit connected to said first tube to receive anabrupt potential variation oi one sense in response to conduction bysaid first tube, and further connected through said first;

tube to said second tube to receive an abrupt variation in potential ofthe opposite sense in re-' sponse to conduction by said second tube,means for applying a triggering signal to the grid of said first tube,and means coupling the-grid of} said second tube to said output circuit,said last named means operative to couple a controllable portion of thepotential variation received by said output circuit in response toconduction by said,

trolled gas tubes connected to said operating poi,

tential, an output circuit connected to said first tube to receive anabrupt potential variation of one sense in response to conduction bysaid first tube, and further connected through said first tube to saidsecond tube to receive an abrupt variation in potential of the oppositesense in response to conduction by said second tube, means for applyinga triggering signal to the grid of said first tube, means for applying acontrollable amplitude triggering signal to the grid of the second tubesimultaneously with the establishment of conduction in said first tube,and a quenching circuit operatively associated with said tubes fordeionizing the same subsequent to the establishment of conduction insaid second tube.

6. A pulse generator comprising, an impedance element, means including aswitch circuit connected to said element operative upon closure of theswitch circuit to produce a potential variation of one sense across saidelement definitive of the leading edge of a pulse, a gaseous dischargedevice connected to said element through said switch and operative uponconduction to produce an abrupt potential variation of the oppositesense across said element, and means coupling a portion of the leadingedge of the pulse appearing across said impedance element to saidgaseous discharge device as a triggering signal whereby the ionizationtime of said device functions to control the time duration of the pulse.

7, A pulse generator comprising, an impedance element, means including aswitch circuit connected to said element operative upon closure of theswitch circuit to produce a potential variation of one sense across saidelement definitive of the leading edge of a pulse, a gridcontrolledgaseous discharge device connected to said element through said switchand operative upon conduction to produce an abrupt potential variationof the opposite sense across said element, means coupling a portion ofthe leading edge of the pulse appearing across said impedance element tothe grid of said device as a triggering signal whereby the ionizationtime of said device functions to control the time duration of the pulse,and a quenching circuit operative to deionize said device following thestablishment of conduction therein. i

GEOFFREY B. PARKINSON,

REFERENCES CITED The following references are of record in the file ofthis patent: 1

UNITED STATES PATENTS Number Name Date 1,691,395 Langmuir Nov. 13, 19282,236,015 Sonnentag Mar. 25, 1941 2,394,389 Lord Feb. 5, 1946

